The manufacture of microelectronic devices may involve processing in-process precursors (also referred to as workpieces herein) of these devices with an acid chemistry. Acid chemistries may be used for a variety of purposes. An exemplary use involves removing photoresist or photoresist residues from the workpieces.
A variety of acid chemistries are known. Exemplary acid chemistries include aqueous phosphoric acid, aqueous mixtures including phosphoric acid and sulfuric acid, aqueous sulfuric acid, aqueous mixtures including sulfuric acid and an oxidizing agent such as a peroxide or ozone; nitric acid; combinations of these, and the like. Mixtures of sulfuric acid and hydrogen peroxide are known as SPM chemistry or, alternatively, piranha chemistry.
After acid treatment, it is desirable to rinse workpiece surfaces thoroughly to remove the acid chemistry and/or acid by-products such as salts thereof. Residual acid or salts of acids left on a workpiece surface can cause particle contamination, haze, yield losses, etc.
One way to assess whether workpieces have been rinsed sufficiently following an acid treatment involves assessing whether workpieces develop a haze after sitting for a period of time, e.g., 1 to 24 hours, following the treatment regime. Development of a haze on the workpiece surface generally indicates that the acid chemistry and by-products thereof, such as salts, have not been effectively rinsed from the workpiece surface. Haze may be detected using a laser-based, light scattering detection instrument. Such an instrument scans the surface being evaluated. Light is scattered by particles on the surface. Scattered light is counted and corresponds to the number of particles on the surface. High particle counts, e.g., particle counts of about 400 or higher with a measurement sensitivity of 45 nm and larger, indicate haze. In many cases, it is unacceptable to practice a treatment that allows such a haze to develop. An absence of a haze after sitting for such a time period indicates that the workpiece has been treated, cleaned, and rinsed effectively. Haze assessment is useful to assess rinsing performance.
One strategy to remove acid involves rinsing workpieces with water. When using water alone for rinsing, substantial volumes of water may be needed to effectively rinse the workpiece surfaces. This not only uses a substantial amount of water, but rinsing merely with water alone can take too long to achieve desired throughput in some applications.
Treatments that use less rinsing fluid and/or that accomplish rinsing faster generally involve neutralizing and removing the acid and salts thereof using a suitable neutralizing chemistry often in combination with one or more water rinses.
For example, aqueous mixtures including ammonia and/or another alkaline reagent have been used to neutralize and remove acids and acid salts from workpiece surfaces. One example of aqueous ammonia chemistry is generally referred to as the SC1 chemistry. This chemistry is prepared by combining ingredients including aqueous ammonia (generally in the form NH4OH in aqueous solution), aqueous hydrogen peroxide, and water. A typical SC1 formulation includes one part by volume aqueous ammonium hydroxide (29% by weight ammonium hydroxide), 4 parts by volume hydrogen peroxide (30% by weight peroxide), and 70 parts by volume water. Other formulations that are more concentrated or more dilute with respect to ammonium hydroxide and/or peroxide also have been used.
The SC1 chemistry often is used in combination with water rinse(s). An integrated treatment to remove resist on the front side of a workpiece therefore might involve a treatment sequence in which the front side of the workpiece is treated with an SPM reagent. This is followed by rinsing the front side with water. Then, the front side of the workpiece is treated with an SC1 reagent. This is followed by rinsing the front side with water again. The workpiece is then dried. Some conventional processes treat the workpiece surface with aqueous peroxide or other oxidizing reagent in order to make the rinsing/neutralizing more effective.
Unfortunately, many materials are sensitive to and can be damaged by acid neutralizing chemistries such as the SC1 chemistries. Exemplary materials that are sensitive to SC1 chemistries and ammonia chemistries in general include metal silicides, particularly metal silicides incorporating nickel and platinum. Other ammonia-sensitive materials include oxides, nitrides, silicon, metals, combinations of these, and the like.
Thoroughly rinsing the front side of the workpiece with water has been used as one alternative to remove acid and acid by-products. On the one hand, thoroughly rinsing the workpiece front side with water initially appears to rinse the surface quite effectively. On the other hand, it has been observed that a haze may still develop on the surface anyway.
Therefore, there is a strong need for treatment strategies that reduce haze without unduly damaging sensitive features.